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BACKGROUND OF THE INVENTION
The present invention relates to a tire for a vehicle and process for manufacturing a tire.
Patent FR-A-1 169 474 describes a tire without bead wire, having,
at chat location which is in mounting contact with the wheel rim,
small plies of cables or cords which are parallel between
themselves within each ply and are significantly inclined on the
parallel to the joint, the various plies being at cross
orientations to one another. The aim of this patent is to
facilitate the production of this tire thanks to_ the absence of
bead wire that doesn't need to be produced. However the
manufacture of such a tire does present problems as it-, is difficult to secure the satisfactory holding up of its elements along the stages of building up, of conformation and of vulcanization, and once completed the tire does not allow for a satisfactory rolling endurance.
SUMMARY OF THE INVENTION
The aim of this invention is to propose a tire without bead wire, having a satisfactory rolling endurance...
Another aim of this • invention is to propose a manufacturing process for such a tire. The present process has the interest of being simpLe and economical, at the same time as it allows for the precise positioning and holding up of the elements of the tire during the times of the different stages of its production.
According to the present invention there is provided a tire for a vehicle comprising a crown, two bead portions and at least a carcass ply extending from one bead portion to the other, said at least a carcass ply comprising reinforcing cords oriented in a radial direction, characterized by:
[a] each said bead portion has an annular member having a resistance to rupture in traction in its longitudinal direction, the axis of the said annular member being the axis of the tire revolution;
[b] each said bead portion has at least two contiguous members called
"reinforcing members" placed in contact with said annular member
or close thereto, each of said reinforcing members comprises
parallel reinforcement cords, crossed from ply to ply; in each said
reinforcing member, an angle alpha (a) is an acute angle formed at
any point of the cord, by the cord direction and the tangent to a
circle having as an axis the revolution axis of the tire and passing
through this point on the cord, said angle a conforming to the
relation 0
the reinforcing members are substantially parallel between
themselves;
[c] the group of reinforcing members has a resistance to rupture, in
traction, measured in its longitudinal direction, greater than the
resistance to rupture in traction of said annular member;
[d] the carcass ply winds around the annular member in each said
bead portion;"
[e] the reinforcing members have their upper ends placed in the bead
portion at different heights.
The invention also provides a process for manufacturing the above-mentioned tire the process comprises:
[a] disposing on a tire building drum, an annular member having a
resistance to rupture in traction in the longitudinal direction, the
axis of this element being the axis of the drum rotation;
[b] disposing on said tire building drum, at least two contiguous
members, called "reinforcing members', in contact with the
annular member or close to it; these reinforcing members each
have reinforcing cords parallel between themselves in each said
member and crossed from member to member; said reinforcing
members having a resistance to rupture in traction, measured in
the longitudinal direction, greater than the resistance to rupture in
traction of said annular member;
[c] disposing on said tire building drum, at least one carcass ply
comprising reinforcing cords placed substantially in the directional
sense of the generatrices of the tire building drum;
[d] conforming the tire in such a way that in each reinforcing member
the angle alpha a conforms to the relation 0
being the acute angle formed, at any point of a.ny member cord, by
the direction of the cord and the tangent to a circle having as an
axis the revolution axis of the tire, passing through this point of
the cord, the measurement being taken at the area where the
reinforcing members are substantially parallel between themselves.
[e] vulcanizing the tire.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention will now be clearly explained with reference to the accompanying schematic drawings in which:
figure 1 shows the radial cross section of a tire conforming with the invention, having two bead portions;
figure 2 shows, in more detail, the radial cross section of one of the tire bead portions shown in figure 1;
- figure 3 shows the profile of part of the bead portion shown
on figure 2;
- figure 4 shows the radial cross section, of a bead portion of
another tire conforming to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows a pneumatic tire 1 conforming to the invention. Figure 1 is a radial cross section, that is to say, a cross section as seen through, a plane passing through the rotation axis of the tire 1, this axis not shown on figure r, being parallel to straight line D. This tire 1 comprises a crown 2, reinforced in a known way by two belt packages 21,22, two sidewalls 3, and two
bead portions 4. Each bead portion 4 comprises a reinforcing package 40 which will be described in more detail later.
A radial carcass ply 5 extends from one bead portion 4 to the other, crossing crown 2 and sidewalls 3.
Tire 1 is mounted on the wheel rim 6, the equatorial plane of the tire being schematically shown by line xx, this plane passing through the middle of crown 2 and being perpendicular to the rotation axis of the tire. Figure 2 is a more detailed representation of bead portion 4 in tire 1. This bead portion 4 comprises an annular member 7 comprised of, as an example, an annular cord, the axis of the circle described by the annular cord being the revolution axis of the tire.
Two adjacent reinforcing members 8 and 9 have their respective inferior ends 8i, 9i in contact with the annular member 7 and these members extend above this annular member 7, that is to say, they are closer to crown 2 than member 7. Each member 8, 9 comprises a rubber composition 80, 90 in which are placed reinforcement cords 81, 91. A reinforcing member 10 surrounds member 7 and both members 8, 9, in thus forming two basic plies 1OA, 10B which are applied against members 8, 9 which are themselves thus sandwiched between basic plies 10A, 10B, the plies in contact 10A, 8, 9, 10B, referred to from now on as the "reinforcing members", being thus substantially parallel between themselves. Ply 10 comprises a rubber composition 100 in which are placed reinforcement cords 101. The assembly comprising member 7 and reinforcing members 10A, 8, 9, 1OB is referred to as 40, and the assembly of all these members, excluding member 7, is referred to as 40A.
In any given reinforcing member 8, 9, 10A, 10B, the cords within it are parallel between themselves and determine an acute angle alpha a which is formed at any given point of the cord between the cord longitudinal direction and that of the tangent to a circle having as an axis the revolution axis of the tire arid passing through this point. Figure 3 shows the profile view of a portion of the basic ply 1OB according to a direction parallel to the revolution axis of tire 1. A substantially rectilinear portion of the cord 101 can be seen on this figure, represented by the straight line segment lOla and part of a circle C passing
through a point P of this portion of the cord, the circle C having as its axis the revolution axis of the tire 1, the tangent to this circle C at P being referred to as T. The angle alpha a is thus the acute angle determined by T and lOla, the measure being taken at the place where members 10A, 8, 9, 10B are substantially parallel between themselves.
For each member 10A, 8, 9, 10B the angle alpha a varies as a function of the position of point P, but it is in any case always superior to 0 degree and at most equal to 10 degrees.
The cords in a reinforcing member are at a cross orientation with the cords of the adjacent reinforcing member or members, that is to say, the cords of two contiguous reinforcing members are not parallel to each other. Thus, for instance, cords 81 of reinforcing member 8 are crossed with cords 101 of the contiguous member 10A and with cords 91 of contiguous member 9; cords 101 in member 10A being crossed with cords 101 of member 10B as members 10A, 1OB are constituted by the turn-up of the same member 10 about the member 7.
The expression "cord" must be understood in a very general meaning for member 7 and for cords 81, 91, 101 as such a cord can be made of a single monofilament or multifilament cord or by the combination of such cords twisted together, forming in particular cables or plied yarns. The material used for these cords can vary, it can be metallic for example, notably steel, it can be organic polymer, for example, cellulose material, polyester or polyamide non aromatic or aromatic, notably aramid cords. It can also be mineral, for example, glass or carbon, each cord being possibly composed of plurality of such materials.
The annular member 7 has a resistance to rupture in traction measured in the longitudinal direction substantially inferior to that necessary for a bead wire in a known tire of the same dimension, and the assembly of reinforcing members 40A has a resistance to rupture in traction measured in the longitudinal direction, at least equal to that necessary for a bead wire in a known tire of the same dimension. By "longitudinal direction", it is to be understood as that of a circle having as an axis, the revolution axis of the tire, and passing through the bead wire in the case of a known tire, or through the group of reinforcing
members, in the case of the tire conforming with the invention. The mechanical resistance of these reinforcing members is thus the essential contribution to the mechanical resistance of the reinforcing package 40 comprising member 7 and members 8, 9, 10, which allows this package to replace the bead wire of a conventional tire.
The carcass ply 5 surrounds package 40 and thus also member 7. This carcass ply 5 comprises, as is known, a rubber composition 50 in which reinforcement cords 51 are placed, the name "cords" having the broad meaning above mentioned. For clarity's sake, only a portion of cord 51 is shown on figure 2 . The modulus of the rubber composition 50 is preferably noticeably inferior to •chat of the rubber compositions 80, 90, 100. Between carcass ply 5 and group 40A, two rubber compositions 11, 12 are placed, these being the so-called decoupling rubber compositions. The value M10 of compositions 11, 12 is preferably comprised between the value of rubber composition 50 on one hand and the value of rubber composition 80, 90, 100 on the other hand.
In what follows, for a given rubber composition, M10 represents the tensile stress at an elongation of 10%, this stress being determined according to norm AFNOR-NF-T46-002 of September 1988, under normal temperature and normal hygrometric conditions as defined by norm AFNOR-NF-T40-101 of December 1979. The values of M10 of rubber compositions 80, 90, 100 can be identical or different and the values of M1O of rubber compositions 11, 12 can also be identical or different.
On the layout of figure 2, the ends of members 8,9 opposed to member 7 are referred to as 8a, 9a. In the same way the ends of basic plies 10A, 10B, not in contact with member 7, are referred to respectively as lOa, lOb. All the ends 8a, 9a, lOa, lOb are called superior ends and are placed in bead portion 4.
Rubber composition 11 is placed outside package 40, against the superior part of member 10A and continues above package 40 in sidewall 3, and rubber composition 12 is applied between the ends lOa and lOb, and is in contact with the four members 10A, 8, 9,
10B.
All these superior ends are placed at different heights on the layout of figure 2 : when one moves toward the crown in the direction of vertical arrow F parallel to the equatorial plane posed at vertical, one finds at increasing heights and in this order the ends lOb, 9a, 8a, lOa, that is to say, the thickness and thus the rigidity of assembly 40 diminishes as one gets closer to the crown, in the direction of arrow F. Increasing heights HlOb, H9a, H8a, HlOa, correspond respectively to ends lOb, 9a, 8a, 10a, and are delineated on a vertical line delta A extending from the horizontal line delta 5 passing through the inferior end 4i of the bead portion 4.
Tire 1 can be manufactured in the following way on a tire building drum. One places the carcass ply 5, then the decoupling rubber composition 11 followed by member 10. Then one places annular member 7 on top of member 10, for example, by winding in circles one or several turns of a rubber coated cord to form the member. One then applies on member 10, contiguous to member 7, the two members 8, 9 superimposed on each other, the ends of which 8a, 9a, are placed in the direction of the center of the tire building drum. One then accomplishes a turn up of carcass ply 5, and of member 10 around member 7 and members 8,9. One finishes the manufacturing process of the tire by building, conformation, and vulcanization in the conventional way. The wraps of member 7 are well bonded together, and with the rest of the tire, without any particular attachment means, thanks to the tackiness of the rubber composition that surrounds the cord constituting member 7.
The annular member 7 has a resistance to rupture in traction measured in the longitudinal direction, preferably inferior to 500 daN, and even more preferably inferior to 300 daN, that is to say, this member has a mechanical resistance largely inferior to that necessary for a bead wire, the tire 1 being thus without a conventional bead wire. However this resistance to rupture in traction is chosen so that it allows for the building up, the turn up, the conformation and vulcanization, above described, that is to say that the member 7 has a level of mechanical resistance largely inferior to that of a classical bead wire, as member 7 does not play the role of a bead wire, but rather of a member allowing the placement of reinforcing members 10A, 8, 9, 10B in relation to each other.
The assembly 40A of reinforcing members has a resistance to rupture in traction measured in the longitudinal direction, superior to 800 daN and more preferably, superior to 1000 daN.
As an example tire 1 has the following characteristics:
- Dimension 175/70-13.
- Crown plies 21,22: known plies comprising steel reinforcement
cables at a 21 degree angle with the equatorial plane, and
being crossed from ply to ply.
- A carcass ply 5: classical ply having cords 51 in polyester;
value of M10 of rubber composition 50: 0.3MPa.
-- An annular member 7: two wraps of a cord constituted of a plied yarn of aramid; resistance to rupture in traction: 100 daN, global resistance, in the longitudinal direction of member 7 being thus 200 daN.
- Reinforcing members 10A, 8, 9, 1OB: identical members having
aramid cords;
.resistance to rupture in traction, measured in each member in the cord direction of the member: 5000 daN/dm of the width of the member, the resistance to rupture in traction measured in the longitudinal direction of assembly 40A being around 4500 daN;
.value of M1O of rubber tissues 80, 90, 100 (identical): 2.4 MPa.
Decoupling rubber compositions 11, 12 (identical):
.value of M10: 0.6 MPa.
.these rubber compositions 11, 12 have, for example, an hysteretical loss, measured at 60 degrees C, inferior to that of rubber compositions 80, 90, 100, 50.
Tire weight: 6.3 kg.
This tire is rolled at a speed of 215 Km/h until failure occurs. When it does, one observes that it is due to the failure of crown 2, not due to the failure of assembly 40.
Furthermore, one manufactures a known tire of the same dimension 175/70-13, and identical to the tire of the invention except that the reinforcing assembly 40 is replaced by a classical metal bead wire, the resistance to rupture in traction of which, measured in the longitudinal direction, is 2000 daN.
The weight of this witness tire is 6.8 Kg, that is to say that the invention procures a weight loss superior to 7%.
This witness tire is rolled under the same condition as the one conforming to the invention and one observes that its performance characteristics are analogous to those of the tire of the invention.
The invention presents the following advantages:
the manufacture of the tire is simple and economical as the assembly 40 is formed directly on the tire building drum, no previous bead wire manufacture is needed;
the presence of annular member 7 allows for a precise positioning of reinforcing members IDA, 8, 9, 10B, easily reproduced without any other holding element;
furthermore, the presence of decoupling rubber compositions 11, 12 as well as the staging of the superior ends of the plies in the bead portions allows for shearing action to occur between the radial carcass ply and the assembly 40, rigid in its longitudinal direction, as well as a progressive transition between the rigidity of the bead portions 4 and the flexibility of sidewalls 3;
- when non metallic materials are used to manufacture the
assembly 40 there is a considerable loss of weight in
comparison to classical tires with metallic bead wires;
- the tire without bead wire allows for an endurance comparable
to that of a classical tire with bead wire in spite of the
simplicity of its manufacture.
Obviously, the invention applications are not limited to the previously described embodiments.
For example, it would be possible to have an assembly 40 with only two reinforcing members such as 8, 9, or members 10A, 10B.
Also members 8, 9, could be placed in the proximity of member 7, for example, by being separated from this member by a rubber composition of slight thickness, for instance inferior to 5 mm, and members 8, 9, 10 could be different, with, for example, rubber compositions of different modulus and only one decoupling rubber composition could be used.
Members 8, 9, furthermore, could be manufactured by folding a single ply. One can anticipate cases in which the carcass ply is placed between reinforcing members, as seen on figure 4, where carcass ply 5-1 is directly wound around the annular member 7-1, two reinforcing members 8-1, and 9-1 are wound around carcass ply 5-1 and member 7-1. In this case, at the time of manufacture of the tire, one disposes on the tire building drum the stacking of the plies 9-1, 8-1, decoupling rubber composition 11-1, ply 5-1 and member 7-1, all in this order.
We claim: -
1. A tire for a vehicle comprising a crown, two bead portions and at least a carcass ply extending from one bead portion to the other, said at least a carcass ply comprising reinforcing cords oriented in a radial direction, characterized by:
(a) each said bead portion has an annular member having a
resistance to rupture in traction in its longitudinal direction,
the axis of the said annular member being the axis of the tire
revolution;
(b) each said bead portion has at least two contiguous members
called "reinforcing members" placed in contact with said
annular member or close thereto, each of said reinforcing
members comprises parallel reinforcement cords, crossed
from ply to ply; in each said reinforcing member, an angle
alpha (a) is an acute angle formed at any point of the cord,
by the cord direction and the tangent to a circle having as an
axis the revolution axis of the tire and passing through this
point on the cord, said angle a conforming to the relation
0
reinforcing members are substantially parallel between
themselves;
(c) the group of reinforcing members has a resistance to rupture
in traction, measured in its longitudinal direction, greater
than the resistance to rupture in traction of said annular
member;
(d) the carcass ply winds around the annular member in each
said bead portion;
(e) the reinforcing members have their upper ends placed in the
bead portion at different heights.
2. Tire as claimed in claim 1, wherein the ratio between the resistance
to rupture of the reinforcing members to the resistance to rupture of
the annular member is greater or equal to 8:3.
3. Tire as claimed in claim 1, wherein the ratio between the resistance
to rupture of the reinforcing members to the resistance to rupture of
the annular member is greater or equal to 10:3.
4. Tire as claimed in any one of claims 1 to 3, wherein a carcass ply is
wound around the group of reinforcing members.
5. Tire as claimed in any one of claims 1 to 3, wherein at least one
reinforcing member is wound around the carcass ply and the
annular member.
6. A process for manufacturing a tire as claimed in claim 1, said process comprising the following steps:
[a] disposing on a tire building drum, an annular member
having a resistance to rupture in traction in the longitudinal
direction, the axis of this element being the axis of the drum
rotation;
[b] disposing on said tire building drum, at least two contiguous
members, called "reinforcing members', in contact with the
annular member or close to it; these reinforcing members
each have reinforcing cords parallel between themselves in
each said member and crossed from member to member;
said reinforcing members having a resistance to rupture in
traction, measured in the longitudinal direction, greater than
the resistance to rupture in traction of said annular member;
[c] disposing on said tire building drum, at least one carcass ply
comprising reinforcing cords placed substantially in the
directional sense of the generatrices of the tire building
drum;
[d] conforming the tire in such a way that in each reinforcing
member the angle alpha a conforms to the relation 0
a
any member cord, by the direction of the cord and the tangent to a circle having as an axis the revolution axis of the tire, passing through this point of the cord, the measurement being taken at the area where the reinforcing members are substantially parallel between themselves.
[e] vulcanizing the tire.
7. A tire for a vehicle substantially as hereinbefore described with
reference to and as illustrated in the accompanying drawings.
8. A process for manufacturing a tire substantially as hereinbefore
described with reference to the accompanying drawings.
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